Delivery system for magnetorheological fluid

ABSTRACT

A magnetorheological fluid delivery system includes a mixing and tempering vessel. Fluid is admitted to the vessel via a plurality of tangential ports, creating a mixing of the fluid in the vessel and promoting homogeneity. Fluid may be reconstituted in the vessel by metered addition of carrier fluid. A fixed-speed centrifugal pump disposed in the vessel pressurizes the system. Fluid is pumped through a magnetic-induction flowmeter and a magnetic flow control valve having solenoid windings whereby MR fluid is magnetically stiffened to restrict flow. A closed-loop feedback control system connects the output of the flowmeter to performance of the valve. A nozzle having a slot-shaped bore dispenses MR fluid for re-use in the work zone. A planar-diaphragm flush-mounted pressure transducer at the entrance to the nozzle and flowmeter inferentially measure relaxed viscosity and provide signals to a computer for dispensing metered amounts of carrier fluid into the mixing vessel to assure correct composition of the reconstituted fluid as it is dispensed.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to methods and apparatus forcirculating and dispensing fluids; more particularly, to methods andapparatus for circulating and dispensing fluids havingmagnetorheological properties; and most particularly, to methods andapparatus for managing and metering magnetorheological fluids being usedin a magnetorheological finishing apparatus.

[0003] 2. Discussion of the Related Art

[0004] It is well known in the art of finishing and polishing surfacesto use, as a finishing agent, particulate fluid suspensions havingmagnetorheological properties. Such fluids, known as magnetorheologicalfluids (MR fluids), comprise magnetically soft particles which canbecome oriented and magnetically linked into fibrils in the presence ofa superimposed magnetic field, thereby increasing the apparent viscosityof the fluid by many orders of magnitude. Such increase is known asmagnetic “stiffening” of the MR fluid. It is further known toincorporate finely-divided abrasives into MR fluids used in finishingand polishing to increase the rate of removal of material.Non-stiffened, or magnetically relaxed, MR fluid can be stored andpumped as a low-viscosity fluid, having a viscosity typically of about50 cp or less, then stiffened to a semi-rigid paste of 10⁵ cp or more ina magnetic work zone for finishing or polishing, then relaxed againoutside the work zone for collection, reconditioning, and reuse.Apparatus and methods for magnetorheological finishing and for deliveryof MR fluids are disclosed in, for example, U.S. Pat. No. 5,951,369issued Sep. 14, 1999 and U.S. Pat. No. 5,971,835 issued Oct. 26, 1999,both to Kordonski et al., the relevant disclosures of which are hereinincorporated by reference.

[0005] MR fluid finishing apparatus typically includes a fluid deliverysystem (FDS) for dispensing MR fluid onto a rotating carrier surface,whereon the fluid is carried into and out of the work zone. MR fluid isa relatively unstable suspension because the magnetic particles tendreadily to agglomerate and to settle out of suspension and therebystagnate. Thus, a primary concern in configuring an FDS for MR fluid iskeeping the fluid relatively homogeneous in the system, and very highlyhomogeneous at the point of dispensing into the work zone. An FDS mustreceive spent fluid from the work zone, recondition the fluid for reuseas by adjusting the temperature and viscosity, homogenize the adjustedfluid, and redispense the fluid into the work zone at a controlled flowrate. A suitable prior art FDS is disclosed in U.S. Pat. No. 5,951,369incorporated above.

[0006] Because of these various requirements, the prior art FDS isrelatively complex and includes a first peristaltic pump for removingspent fluid from a scraper at the work zone and returning the fluid to areservoir; a mixer in the reservoir for rehomogenizing the fluid; atempering subsystem at the reservoir for cooling the fluid, which tendsto become heated in the work zone; a second peristaltic pump andcylindrical nozzle having a fixed restriction for redispensing thefluid; a pulse-dampener for removing pulses generated by the pumps; anda viscosity measuring and correcting subsystem. Flow may be controlledby manually setting the speed of the second pump, and preferably ismonitored via a magnetic induction flowmeter.

[0007] Several problems are presented by the prior art FDS.

[0008] First, the system is cumbersome, as it is essentially anassemblage of discrete components, each intended to perform a singletask. Thus, the system is wasteful of space.

[0009] Second, the flow control system requires a positive-displacement(PD) pump. Some known PD pumps such as gear pumps are unsuited to thetask of pumping MR fluids. A peristaltic pump can meet thepositive-displacement need over a short period of time; however, thepulsating output mandates the pulse-dampening apparatus already noted,and the delivery lines within the pump are subject to fatigue and mustbe replaced frequently.

[0010] Third, correct composition of the MR fluid being redispensed isinferred from an inline viscometer which incorporates a cylindricalnozzle that, for flow reasons, must be relatively long and thus iscumbersome. In the flow and composition control strategy employed, aconstant input pressure at the entrance to the nozzle and a constantflowrate at the flowmeter indicate a constant viscosity and henceconstant composition of the fluid being dispensed.

[0011] What is needed is an improved fluid delivery system for managingMR fluid in an MR finishing apparatus wherein flow is inherently smooth,pulsations are not generated, and pulsation dampening is unnecessary;wherein the dispensing flow is maintained at a desired flowrate by aclosed-loop flow control subsystem; wherein the composition of the MRfluid is automatically corrected to aim during a reconditioning step;wherein the sizes of components such as a dispensing nozzle areminimized; and wherein mixing, tempering, and pressurizing of MR fluidis performed in a single vessel.

[0012] It is a primary objective of the invention to provide a simple,compact fluid delivery system for managing and dispensingmagnetorheological fluid for use by a magnetorheological finishingapparatus.

SUMMARY OF THE INVENTION

[0013] Briefly described, a magnetorheological fluid delivery system inaccordance with the invention comprises various elements connected byconduit means, including a mixing and tempering vessel. Fluid beingreturned from use in a work zone is admitted to the vessel via aplurality of tangential ports near the bottom of the vessel, creating amixing of the fluid in the vessel and thus promoting homogeneity. Fluidmay be reconstituted in the vessel by metered addition of carrier fluidto compensate for carrier fluid lost in the work zone. A centrifugalpump, preferably operating at a fixed speed, collects the fluid from thevessel and pressurizes the system. Preferably, the pump is disposed inthe vessel. Fluid is fed through a magnetic-induction flowmeter and amagnetic valve having solenoid windings whereby fluid may becontrollably stiffened and thus flow restricted by the associatedviscous drag created in the bore of the valve. A closed-loop feedbackcontrol system connects the output of the flowmeter to performance ofthe valve. A nozzle having a slot-shaped bore dispenses MR fluid forre-use in the work zone. A flush diaphragm pressure transducer at theentrance to the nozzle inferentially measures relaxed viscosity andprovides signals to a computer for dispensing metered amounts of carrierfluid into the mixing vessel to assure correct composition of thereconstituted fluid as it is dispensed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The foregoing and other objects, features, and advantages of theinvention, as well as presently preferred embodiments thereof, willbecome more apparent from a reading of the following description inconnection with the accompanying drawings in which;

[0015]FIG. 1 is a schematic view of a prior art fluid delivery systemfor magnetorheological fluids, substantially as disclosed as FIG. 10 inU.S. Pat. No. 5,951,369;

[0016]FIG. 1a is a cross-sectional view of a prior art nozzle useful inthe delivery system shown in FIG. 1;

[0017]FIG. 2 is a schematic view of an improved fluid delivery system inaccordance with the invention;

[0018]FIG. 3 is an isometric view, partially in cutaway, of amixing/tempering vessel and a pressurizing pump;

[0019]FIG. 4 is a plan view of a magnetic valve;

[0020]FIG. 5 is a cross-sectional view taken along line 5-5 in FIG. 4;

[0021]FIG. 6 is a schematic cross-sectional view of the valve shown inFIGS. 4 and 5, showing the direction and intensity of magnetic fluxwithin the valve; and

[0022]FIG. 7 is an isometric view, partially in cutaway, of an improvedviscometric nozzle in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0023] The benefits and advantages of a magnetorheological fluiddelivery system in accordance with the invention may be betterappreciated by first considering a prior art system.

[0024] Referring to FIG. 1, a prior art fluid delivery system 10 (FDS)is shown for providing MR fluid 11 to a carrier surface 12 of amagnetorheological finishing apparatus (not otherwise shown) at aconstant aim flow rate and viscosity; for recovering MR fluid from thecarrier surface; and for conditioning recovered MR fluid for re-use. MRfluid 11 is scraped from the carrier surface 12 by scraper 14 andreturned via line 16 to an inline mixing and tempering vessel 18 whereinagglomerates are broken up, carrier fluid is replenished as describedbelow, and the reconstituted MR fluid is re-tempered to an aimtemperature. A prior art system typically includes a supplementaryperistaltic pump 20 to acquire the spent MR fluid from scraper 14 anddeliver it to vessel 18. Retempered MR fluid is withdrawn from vessel 18by a primary peristaltic delivery pump 22 and is delivered through aninline magnetic-induction flowmeter 24. The output of peristaltic pumpsis cyclic and therefore a pulse dampener 26 is required in the fluiddelivery system downstream of pump 22. Flowmeter 24 and the drive forpump 22 are connected to a computer 28 which sets a flow aim and therotational speed of the pump. From the flowmeter, MRF passes throughnozzle 30 and is discharged for work onto carrier surface 12.

[0025] Referring to FIG. 1a, prior art nozzle 30 is an inline capillaryrheometer or viscometer at the discharge end of the fluid deliverysystem and comprises a capillary tube 32 formed of a non-magneticmaterial, for example, stainless steel or ceramic, having a length todiameter ratio preferably greater than about 100:1. Tube 32 issurrounded by a magnetic shield 34 formed preferably of a magneticallysoft material, for example, low-carbon cold rolled steel. Tube 32 andshield 34 are spaced apart by one or more non-magnetic centering spacers36 and by a non-magnetic transition piece 38 for smoothly narrowing theMR fluid flow from the diameter of the supply line 40 to the diameter oftube 32. Disposed between supply line 40 and transition piece 38 is apressure transducer 42 having a diaphragm 44 for sensing line pressureat the entrance to the capillary tube and sending a signal thereof tocomputer 28. Since nozzle 30 is disposed at the end of the deliveryline, the pressure drop through the nozzle may be measured relative toambient pressure, and thus only one pressure sensor is required.Computer 28 is programmed with an algorithm for calculating MR fluidviscosity as a function of pressure and flowrate through nozzle 30. Whena predetermined upper viscosity control limit is exceeded, computer 28signals metering pump 46 to inject a computer-calculated replenishingamount of carrier fluid into mixing/tempering chamber 18 where the fluidis mixed into the recirculating MRF.

[0026] Referring to FIGS. 2 through 7, an improved and compact fluiddelivery system 50 (FDS) in accordance with the invention is shown forproviding MR fluid to a carrier surface 12 of a magnetorheologicalfinishing apparatus (not otherwise shown) at a constant aim flow rateand viscosity; for recovering MR fluid from the carrier surface; and forconditioning recovered MR fluid for re-use. System 50 includessignificant improvements in mixing, pumping, metering, and dispensingover prior art system 10, and is significantly less complex and morecompact. Several components of system 10 are eliminated, includingsupplementary pump 20 and pulsation dampener 26.

[0027] As shown in FIG. 2, MR fluid 11 is scraped from the carriersurface 12 by scraper 14 and returned via line 16 to an improved inlinemixing and tempering vessel 52 wherein agglomerates are broken up,carrier fluid is replenished, and the reconstituted MR fluid isre-tempered to an aim temperature and prepared to be re-dispensed ontocarrier surface 12.

[0028] As shown in FIG. 3, improved vessel 52 includes an insulatingjacket 54 surrounding a mixing chamber 56. Spent MR fluid being returnedfrom scraper 14 is drawn into chamber 56 via at least one passage 58,and preferably a plurality of such passages, extending from a splittingblock 60 on the underside of vessel 52 and entering into chamber 56through jacket 54 at ports 55 near the bottom 62 of the chamber andsubstantially tangential to the inner wall 64 of the chamber. Thisconfiguration causes a high level of swirling agitation of MR fluidwithin chamber 56 without resort to a separate mechanical mixer as isrequired in prior art mixing chambers. MR fluid is drawn into splittingblock 60 from return line 16, wherein the fluid flow is split into aplurality of streams following passages 58. As in the prior art system,replenishing carrier fluid is injected from a source (not shown) viareplenishment pump 46 and line 66 in response to commands from computer28, either into return line 16 as shown in FIG. 2 or directly intovessel 52.

[0029] Disposed within chamber 56 is a centrifugal pump 66 having avertical drive shaft 68 supporting a conventional vaned impeller 70 nearthe bottom 62 of the chamber. Preferably, impeller 70 is vaned on boththe upper and lower surfaces thereof to balance the pumping load and toincrease the output volume. Pump housing 72 surrounds the shaft andimpeller and is closed at its lower end by an end plate 74 having acentral aperture 76 for receiving the outer end of shaft 68 and impeller70 and for admitting MR fluid from the lower part of chamber 56 toimpeller 70. Housing 72 is provided with an inlet passage 78 foradmitting MR fluid from the upper part of chamber 56 to impeller 70. Anoutlet passage 80 extends within housing 72 from the periphery ofimpeller 70 through jacket 54 to the exterior of vessel 52. Housing 72is further surrounded by tempering coils 82 of a conventional liquidheat exchanger tempering system (not shown) for adjusting thetemperature of MR fluid within chamber 56 to a predetermined aim inknown fashion.

[0030] Pump drive 84 is disposed outside and above vessel 52 and iscoupled to shaft 68 via a central bore in housing 72, which housing alsofunctions as the closing cover for vessel 52. Drive 84 is operationallyconnected via conventional interface conversion elements to controlcomputer 28 which may, via connection 85, set and maintain therotational speed of pump 66, preferably at a predetermined fixed speedselected to optimize the output of the pump, for example, 3200 rpm.Alternatively, the speed of the pump may be set manually by conventionalelectromechanical means.

[0031] Referring to FIGS. 3 through 6, a novel magnetic flow controlvalve 86 and a conventional magnetic induction flowmeter 24 are disposedinline downstream of pump 66. Flowmeter 24 senses the flow volume ofmaterial passing therethrough and communicates with computer 28 whichthen sends a controlling signal to valve 86 to adjust the flow sensed byflowmeter 24 to some predetermined aim. The flowmeter, valve, andcomputer thus form a conventional closed-loop feedback control system.Because pump 66 is a centrifugal pump and thereforenon-positive-displacement, unlike prior art peristaltic pump 22,hydraulic slip can occur within the pump, permitting valve 86 simply tothrottle the pump output.

[0032] Magnetic flow control valve 86 comprises a solenoid without anarmature, the MR fluid replacing the armature, and having first andsecond end caps 87,89 having first and second nipples 91,93,respectively for connection of the valve into the FDS. The end caps aremagnetically linked by a cylindrical housing 95 which also functions asa magnetic shunt. Hollow first and second magnet polepieces 88,90,respectively extend axially towards each other from end caps 87,89,respectively, within windings 92 which may be, for example, 1000ampere-turns. Polepieces 88,90 are separated by a non-magnetic spacer 94also within the windings and preferably having an axial bore of the samediameter as the bores in the polepieces, such that the axial passageway96 extending through valve 86 is of a single non-restricted diameter.Spacer 94 forms and fills a magnetic gap between the polepieces. Each ofpolepieces 88,90 is tapered toward the other, preferably conically, onan outer surface thereof as shown in FIGS. 5 and 6, such that magneticflux is directed and concentrated towards the gap, creating a magneticfield 98 within passageway 96 in which the flux lines are substantiallyparallel to the axis of the passageway, as shown in FIG. 6. Inoperation, when the windings are de-energized, passageway 96 exerts lowviscous drag on MR fluid flowing through the valve. Flow through thevalve is limited only by the diameter of passageway 96, the outputpressure of pump 66, and the mechanical restrictions in the FDSdownstream of the valve. When the windings are controllably energized inresponse to signals from computer 28, MR fluid in the magnetic field ismagnetically stiffened within the valve to a higher apparent viscosity,thus creating increased flow resistance due to viscous drag on the wallsof passageway 96. Flow is thus controllably decreased from thenon-energized level. The MR fluid becomes again relaxed, of course, uponpassing out of the valve. By controllably varying the intensity of themagnetic field by varying the current through windings 92, computer 28is able to control the flow through the FDS in response to apredetermined flow aim and to the actual flow as measured by flowmeter24.

[0033] Referring to FIG. 7, an improved dispensing nozzle 30 a is aninline capillary rheometer or viscometer at the discharge end of fluiddelivery system 50 and comprises a barrel 32 a formed of a non-magneticmaterial, for example, stainless steel or ceramic. Barrel 32 a issurrounded by a magnetic shield 34 a formed preferably of a magneticallysoft material, for example, low-carbon cold rolled steel. A non-magnetictransition piece 38 a smoothly narrows the MR fluid flow from thediameter of the supply line 40 into barrel 32 a. Extending throughshield 34 a and barrel 32 a and exposed to the material flowpath is apressure transducer 42 a for sensing line pressure at the entrance tothe capillary tube and sending a signal thereof to computer 28. Sincenozzle 30 a is disposed at the end of the delivery line, the pressuredrop through the nozzle may be measured relative to ambient pressure,and thus only one pressure transducer is required. Computer 28 isprogrammed with an algorithm for calculating MR fluid viscosity as afunction of pressure and flowrate through nozzle 30 a. When apredetermined upper viscosity control limit is exceeded, computer 28signals replenishment pump 46 to inject a computer-calculatedreplenishing amount of carrier fluid into either return line 16 ormixing/tempering vessel 52 wherein the fluid is mixed into therecirculating MR fluid.

[0034] A particular feature and advantage of nozzle 30 a over prior artnozzle 30 is the incorporation of a non-cylindrical slot-shaped flowpassage 100 through barrel 32 a rather than the conventional cylindricalflow passage in nozzle 30. Passage 100 has first and second opposedparallel planar walls 102 having a longer transverse length than thirdand fourth opposed walls 104. A first advantage is that passage 100dispenses MR fluid onto carrier surface 12 as a pre-formed ribbon. Asecond advantage is that pressure transducer 42 a may be mounted in aplanar wall 102 of passage 100, permitting the use of an inexpensiveflush diaphragm 44 a in replacement of the prior art diaphragm 44. Athird advantage is that a slot-shaped passage exhibits increased viscousdrag of the MR fluid because of greater surface area per unit length;therefore, a significantly shorter nozzle can yield a back pressure attransducer 42 a equal to the back pressure present at prior arttransducer 42.

[0035] Pressure drop along a slot-like channel and a round pipe arepresented as follows: $\begin{matrix}{{\Delta \quad P_{slot}} = \frac{2\quad \mu \quad L_{slot}Q}{b^{3}w}} & \left( {{Eq}.\quad 1} \right) \\{{\Delta \quad P_{pipe}} = \frac{8\quad \mu \quad L_{pipe}Q}{\pi \quad R_{pipe}^{4}}} & \left( {{Eq}.\quad 2} \right)\end{matrix}$

[0036] where μ is fluid viscosity, L_(slot) is slot length, b is slothalf-height, w is the width of the channel, L_(pipe) is pipe length, Ris pipe radius and Q is flow rate. When the pressure drop, flow rate,and viscosity in both channels are the same, then $\begin{matrix}{{\frac{2L_{slot}}{b^{3}w} = \frac{8L_{pipe}}{\pi \quad R^{4}}}{or}} & \left( {{Eq}.\quad 3} \right) \\{L_{slot} = {L_{pipe}\frac{4b^{3}w}{\pi \quad R^{4}}}} & \left( {{Eq}.\quad 4} \right)\end{matrix}$

[0037] To provide the same fluid velocity in both channels, thechannels' cross sectional areas must be the same

2b w=3.14R ² and L_(slot) =L _(pipe)(2b ² R ²)  (Eq. 5)

[0038] The cross-sectional area of a cylindrical tube having a radius of1.5 mm is about the same as the cross-sectional area of a slot-shapedpassage having a slot height of 1.5 mm and slot width of 5 mm. Thus, forexample, a prior art cylindrical nozzle 30 having a tube length of 200mm can be replaced with an improved nozzle 30 a having a barrel 32 awith a slot length of about 100 mm. Such a shortening of the nozzlegreatly enhances the desirable compactness of an MR fluid deliverysystem.

[0039] From the foregoing description it will be apparent that there hasbeen provided an improved delivery system for magnetorheological fluid.Variations and modifications of the herein described fluid deliverysystem will undoubtedly suggest themselves to those skilled in this art.Accordingly, the foregoing description should be taken as illustrativeand not in a limiting sense.

What is claimed is:
 1. A system for metering flow of amagnetorheological fluid through a conduit means, comprising: a) meansfor pressurizing said fluid within said conduit means; and b) meansincluding a magnetic valve for controllably varying the flow rate ofsaid pressurized fluid through said conduit means.
 2. A system inaccordance with claim 1 further comprising flow measurement meansserially connected to said magnetic valve for determining said rate offlow.
 3. A system in accordance with claim 2 further comprisingprogrammable control means operationally connected to said flowmeasurement means and to said magnetic valve for adjusting said magneticvalve in response to signals from said flow measurement means to controlsaid rate of flow to a predetermined aim.
 4. A system in accordance withclaim 3 further comprising means connected in said conduit means fortempering said MR fluid.
 5. A system in accordance with claim 4 furthercomprising means connected in said conduit means for mixing said MRfluid.
 6. A system in accordance with claim 5 wherein said means fortempering and said means for mixing and said means for pressurizing areincluded in a single mixing/tempering vessel.
 7. A system in accordancewith claim 1 wherein said means for pressurizing includes a centrifugalpump.
 8. A system in accordance with claim 1 further comprising meansfor replenishment of carrier fluid into said MR fluid.
 9. A system inaccordance with claim 1 further comprising a nozzle for dispensing MRfluid from said system, said nozzle having a non-cylindrical flowpassage.
 10. A system in accordance with claim 9 wherein said flowpassage is slot-shaped in cross-sectional shape.
 11. A system inaccordance with claim 10 wherein said flow passage includes first andsecond parallel planar walls.
 12. A system in accordance with claim 11further comprising third and fourth opposed walls, wherein said firstand second walls are longer in transverse width than said third andfourth walls.
 13. A system in accordance with claim 1 wherein saidmagnetic valve comprises: a) first and second magnet polepiecescoaxially disposed, each having an axial flow passage therethrough, saidpolepieces being axially spaced apart and being tapered on an outersurface thereof towards each other; b) a non-magnetic spacer having anaxial flow passage therethrough and being disposed between said firstand second polepieces; and c) solenoidal electrical windings surroundingsaid polepieces and said spacer for controllably providing a magneticfield within said flow passage in response to energizing signals.
 14. Asystem in accordance with claim 13 wherein said magnetic valve isfurther provided with first and second nipples extending from said firstand second polepieces for attaching said valve into said conduit means.15. A magnetic flow control valve for variably stiffening amagnetorheological fluid passing therethrough to increase viscous dragof the fluid in the valve, comprising: a) first and second magnetpolepieces coaxially disposed and each having an axial flow passagetherethrough, said polepieces being axially spaced apart and beingtapered on an outer surface thereof towards each other; b) anon-magnetic spacer having an axial flow passage therethrough and beingdisposed between said first and second polepieces; and c) solenoidalelectrical windings surrounding said polepieces and said spacer andconnectable to an electrical source for controllably providing amagnetic field within said flow passage in response to energizingsignals.
 16. A nozzle for dispensing magnetorheological fluid,comprising a barrel having a longitudinal flow passage slot-shaped incross-section.
 17. A nozzle in accordance with claim 16 wherein saidpassage includes first and second parallel planar walls.
 18. A nozzle inaccordance with claim 17 further comprising third and fourth opposedwalls of said passage, wherein said first and second walls are longer intransverse width than said third and fourth walls.
 19. A nozzle inaccordance with claim 16 further comprising a magnetic shieldsurrounding said barrel.
 20. A nozzle in accordance with claim 19further comprising a pressure transducer disposed in said slot-shapedpassage.
 21. A fluid delivery system including components interconnectedby tubing for managing the delivery, recovery, and reconditioning ofmagnetorheological fluid for a magnetorheological finishing apparatus,comprising: a) a tempering and mixing vessel having a chamber includingan inner wall and a bottom and having at least one passage entering saidchamber for admission of MR fluid to said chamber, the axis of saidpassage being substantially tangential to said inner wall and proximalto said bottom to cause mixing of said MR fluid, said vessel beingfurther provided with heat exchanging means for tempering the MR fluid;b) a centrifugal pump for pressurizing the MR fluid by pumping the fluidfrom said vessel through said tubing; c) a magnetic flow control valvehydraulically connected in series with said pump; d) a flowmeterhydraulically connected in series with said pump and said valve; e)programmable control means for receiving input signals from saidflowmeter indicative of a rate of MR fluid flow therethrough and forproviding output signals to said flow control valve to adjust said rateof fluid flow to a predetermined rate; and f) nozzle means hydraulicallyconnected in series with said flowmeter for receiving MR fluid therefromand dispensing said fluid to said finishing apparatus.
 22. A system inaccordance with claim 21 wherein said pump is disposed within saidvessel.
 23. A magnetorheological finishing apparatus, comprising a fluiddelivery system including conduit means for managing the delivery,recovery, and reconditioning of magnetorheological fluid, said fluiddelivery system including a) means for pressurizing said fluid withinsaid conduit means; and b) means including a magnetic valve forcontrollably varying the flow rate of said pressurized fluid throughsaid conduit means.